1. Technical Field of the Invention
This invention relates generally to communication systems and more particularly to radio frequency transmissions within such systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
To achieve a high performance radio frequency integrated circuit (RFIC), the gain of the low noise amplifier and the gain of the power amplifier need to be accurately set. In addition, the local oscillation needs to be tuned to a desired frequency. To set the low noise amplifier gain, the signal strength of received RF signals is determined via a power detection circuit. The gain of the low noise amplifier is then set based on the received signal strength. In particular, the larger the signal strength the lower the gain and the lower the signal strength the higher the gain. The gain of the power amplifier is set based on transmit power of outgoing radio frequency signals, which is determined by a power detection circuit. The tuning of the local oscillation is based on a peak determination of the local oscillation.
As such, power detection circuits have an important function within high performance RFICs and have been implemented in a variety of ways. For example, the power detection circuit may include two input transistors, a current source and a low pass filter. The input transistors have their gates coupled to receive opposite phases of a differential signal under test. The sources of the transistors and the input to the low pass filter are coupled to the current source, which is also coupled to ground. The drains of the transistors are coupled to a supply voltage via a resistive load. The output of the low pass filter provides the peak value.
The output of low pass filter is then provided to an analog to digital converter to generate a digital peak value. Typically, the analog to digital converter was off-chip, thus the analog peak detection signal was supplied off-chip, converted to a digital signal, and then provided back to the RFIC.
As the operating rates of RFICs push the limits of the integrated circuit fabrication process (e.g., CMOS technology), such power detection circuits are inaccurate for lower amplitude signals. This inaccuracy results because the power detection circuit is slower than the rates of the RFIC.
Therefore, a need exists for a digital high frequency power detection circuit that is accurate at high operating rates, which push the limits of an integrated circuit technology.